PROJECT ABSTRACT Zn-T8 is a novel autoantigen in type 1 diabetes (T1D). The role of Zn-T8 as a target in MHC class II-mediated islet autoimmunity has remained largely unexplored. To our knowledge, there are no reports on the Zn-T8- specific CD4+ T cell responses in the preclinical phase of diabetes progression. We propose to determine the role of Zn-T8-specific T cell responses in T1D by investigating these responses in islet autoantibody positive family members of T1D patients stratified by a distinct disease risk using PBMC samples from TrialNet Natural History Study. Our hypothesis is that CD4+ and CD8+ T cell responses to Zn-T8 are associated with progression to T1D. Specifically we expect that Zn-T8 specific T cells in the high risk individuals display a memory phenotype associated with recent activation. We also expect that in the high risk individuals both CD4+ and CD8+ T cell responses are more robust and targeted to multiple epitopes. The comparison between high and low risk subjects is expected to reveal a potential regulatory phenotype in the latter, which could discriminate the subjects who are unlikely to progress to the disease despite of the same MHC class II genotypes. Furthermore, we predict that there will be differences in the Zn-T8 epitope utilization and/or T cell reactivity when subjects are stratified by SLC30A8 polymorphism. The overall goal of the project is to provide a novel insight to T cell-mediated autoimmunity in T1D which could be applied for monitoring the disease progression and the immunological outcomes of therapies in clinical trials. Furthermore, improved knowledge of the mechanisms of autoimmune process leading to T1D will contribute to discovery of new therapeutic targets.